What Is The Scariest Thing?

[Michael breathing heavily] [laughing nervously] Everyone is scared of something. But is there something that everyone is scared of? What is the scariest thing possible? ♪ [Michael] So what is the scariest thing? - Is it thunder? - [thunder crackles] Shadows? Being burned alive? [laughs nervously] [laughs evilly] No. It's also not heights or needles, snakes, spiders, sharks-- those things can be scary to some, sure, but not to all.

So here's what I mean by "scariest." I want a thing-- an object, an action, an idea-- that, at my disposal, would be guaranteed to elicit fear and panic in anyone who might happen to walk into this room right now, regardless of how old they were, their cultural background, their abilities, or even their neurology. An adventure towards this ultimate terrible thing must necessarily focus on the womb. No, not the kind you came from, but the womb in which fear itself gestates: the mind. -[wind whistling] -[thunder crashes]

To find the scariest thing, we must understand how fears are born. [thunder crashes] [projector whirring] ♪ Where are we going? [laughs evilly] Don't worry about it. Only two things matter: one, I've got plenty of gas, so what could go wrong? And two, our destination is a little bit spooky and we're gonna learn. Because in order to truly grasp what makes the one true scariest thing, well, we need to dive deeper into how we learn fears.

[monster growling] [Michael] To start out, I commissioned a fear-conditioning demonstration on me. You've probably heard that exposure therapy can help people overcome their fears. Well, the same principles can be used to create fears. Hello, Michael? I'm Dr. Tomislav Zbozinek from Caltech, and today we're gonna do some fear conditioning. Do you have any heart conditions or any serious major medical conditions? - No. - Okay. You've done this to people before. - Hundreds of times. - And they were all okay? They were all okay. Yeah, everything worked out okay. - All right, I'm ready. - Okay, perfect.

[Michael] The protocol for fear conditioning involves my being electrically shocked and startled by the sound of a human scream in connection to visuals I see on a screen. Bioelectric sensors monitor my body's physiological reactions. For example, my perspiration, an indirect measure of fear that you can't consciously control. Is this how you run this at Caltech? - Yes, this is the exact-- - [laughs] Exactly the same way. - Minus the restraints, of course. - Oh, the-- Oh, okay. Yeah. Everything else is solid fear conditioning-- - As your usual--? - Yes. Absolutely. All right, I'm game. Let's help science.

[Michael] The goal of this procedure is to condition me to be scared of something I've never feared before-- a mundane, harmless geometric shape-- something normal people don't find threatening at all. - [electricity crackles, recorded scream] - Aaaah! -[electricity crackles] -[recorded scream] Little bit more scared of the square right now. -[electricity crackles] -[recorded scream] [Michael] A clear pattern emerges. My senses are being assaulted only when the purple square is onscreen. -[electricity crackles] -[recorded scream] [breathing heavily] But am I actually being conditioned to fear a purple square? -[electricity crackles] -[recorded scream]

All right, Michael, you're all done. - Hoo! - How was it? Well, it felt like I was one of Pavlov's dogs. I couldn't help what I was doing, and I was being trained to do it in response to something, and that something was an otherwise very unassuming geometric shape. Exactly. With Pavlov's dogs, he had a bell and food, something positive at the end. But in fear conditioning, we have something aversive and negative at the end. [Michael] And it worked. Once my brain associated the purple square with being shocked, my physiological response to the square went up and stayed up. The mere appearance of a simple geometric shape made me scared enough to break a sweat.

The results show that you physiologically really ramped up to that purple square, specifically. You quickly learned to be afraid on a physical level. You showed fear. I came in here today normal old Michael, but I'm leaving as a brand-new Michael who is afraid of purple squares. The human brain can learn to be afraid of almost anything. [Michael] To better understand how this works, we need to look at what's going on neurologically. What happens in the brain during fear conditioning? Well, what we know is that over evolution, over millions of years, we've developed these defensive circuits in our brain. And the amygdala sits on the front of the memory systems of the hippocampus. And the amygdala seems to play an important role in determining what the danger is of something in the world. It tells us what we should be remembering, what we should be learning, that is important to survival.

[Michael] Our brain actually has two amygdalae-- one in each hemisphere. The function of the amygdalae is at the center of fear research, which covers human behavior ranging from the risk averse... to high risk-takers like free soloist Alex Honnold. Ancient humans who avoided danger and survived long enough to reproduce became our ancestors. They populated the world with creatures like us, organisms that instinctively avoid and are averse to potentially dangerous sensations. Things like pain and being sick, suffocation-- the need to breathe. We don't think those feel good, and you don't have to learn to not like them. Even a newborn is distressed by them, which makes them "innate aversions." Fear is the anticipation of these innate aversions.

[Michael] When the purple square was paired with electric shocks, my amygdala quickly made that association and began consciously and unconsciously arousing fear in me whenever I saw it. For this reason, I want us to think of sensations as flies and our amygdala as a meaty little spider spinning a web of fear. [thunder crackling] [Michael] The web is pre-stocked with our innate aversions. Whenever an experience is associated with an innate aversion, it's like a fly landing on the web. This alerts the amygdala spider, which weaves a powerful connection between that experience and the innate aversion it's associated with. In my case, that innate aversion was pain, which probably isn't the scariest thing for everyone, because, well, some people have a high pain tolerance. Others can learn to suppress their fear of pain. And, of course, some people enjoy pain.

[Michael] But the point is, now that new experience will stay trapped in your web of fear, a new member of the library of things that scare you. To find the scariest thing, we must wander through the darkest recesses of the web. Everything caught in your web of fear is somehow connected to death. Avoiding it-- surviving-- is, after all, what makes fear useful. It's why we are still here today as a species. So if death is at the very center of all of our webs of fear, does that make death the scariest thing? [Michael] Well, although many people say death is their #1 fear, not everyone is afraid of it. Many acts of courage require caring more about others than your own life. Some older people say they're ready to die. And what about those who commit suicide? Sadly, for them, something else was scarier than ending their own life. So death isn't exactly the answer we're looking for.

The scariest thing will be something else on all of our webs that is panic-inducing even to those who want to die. [projector whirring] [car rattling] Dangnabbit! Wouldn't ya know it? I've run out of gas. Guess I'm just gonna have to walk down this desolate, foreboding road in search of a gas station. Luckily, this is just a movie. My rational mind knows that I'm safe, and it will use that to inhibit my amygdala's fear response. [laughs] What a great way to make a horror film scarier, right? Take away one of the rational mind's shields, and the amygdala's fear response won't be as inhibited. What we're about to see really could happen, and perhaps... will.

[Michael] Of course, we don't just learn fears from firsthand experiences. Throughout our history, we have used images and words to teach fears to one another, to prepare the next generation for various dangers. [narrator] These high school boy and girls are having a hop at the local soda fountain, innocent of a new and deadly menace lurking behind closed doors. Marijuana! The burning weed with its roots in hell. Why do humans have to tell stories to share fears from generation to generation and person to person? Language is virtual reality.

So when you tell someone a story, you're not just describing a crocodile, for example, the language in the story has a kind of emotional impact on the listener. So when I tell you some scary story about crocodiles, the amygdala is being activated by the words and the scenarios, allowing the imagination to sort of play with these ideas and scenarios, so you're concocting imagery. So it has a double whammy. And you're getting a very good sense that you should stay away from this kind of thing in the future. As a species, we're very dependent and vulnerable compared to other animals. We don't have sharp teeth and big claws, and we're not really fast-- it takes us years and years to be self-sufficient. So what's happening during those years of development is that we're getting all this information about the environment through stories. And part of that is to know what to be afraid of and what to not be afraid of.

[projector whirring] [echoing] Hello! -Hey, hello! -[bird cawing] Whoo. Okay, being alone is kind of scary, right? But you know what? I'm actually not alone. I am always connected. - [ominous motif plays] - No reception. Of course. I mean, what is this, a horror movie? Yes, it is. And you know what, I'm actually getting a little bit scared right now. A new fear, by the way, has developed in just the last few decades. You see, a while ago, no one had a cell phone. No one was ever connected through the internet constantly. But now many of us, most of us, are. And so that's the new normal, and what's abnormal now is not being connected, not having your phone. Psychologists give that fear a name, it's a real thing that's being studied, and it's called nomophobia.

Anyway, the point is, the scariest thing possible-- hmm, what could it be? Well, an important ingredient might be... [fly buzzing] ...our innate aversion to isolation. Why are we afraid of being alone? Human beings are social animals. We need each other to survive. So if we're alone, it lessens our chances of survival. And there's been a lot of research now that shows that when people isolate socially, it actually leads to things like increased heart problems, increased cancer risk, physical issues, mortality. It is very much directly tied to the sense of survival and avoidance of death.

What I find interesting about isolation is, I think it helps us capture a lot of tertiary-and-beyond fears that don't seem to be directly connected to death, but are, in a way, through isolation. For instance, the fear of public speaking. Yes. Well, that taps into your fear of rejection, and when you feel like people don't like you, you feel alone! And so putting yourself out there, having that possible fear of rejection when you're speaking in public and not knowing how people are gonna perceive you, that's very scary for a lot of people. Which doesn't necessarily mean that you will directly die. However, it connects to our innate aversion to isolation which, through evolution, we have learned is a bad thing that can lead to death. - And so we're afraid of it, avoid it. - Absolutely.

In the very first episode of Mind Field, I spent 72 hours in an isolation chamber. For three days I had no contact with the outside world. I had no clock or window, and the lights never went out. The scariest part, though, wasn't being alone. I could handle that. The worst part was being separated from the natural cycles of the Earth I was so accustomed to. Night and day. Time. The disorientation and helplessness caused by that made me distressed, and may have been a reason why, while in the room, all of my dreams also took place in the same room. I soon became unable to tell the difference between when I was dreaming and when I was awake. I was terrified. Extreme isolation like that is not normal or healthy, but we all respond differently. There are people who love living by themselves in the middle of nowhere.

And with sufficient forewarning of the effects, I think I could have handled it better. So just being all alone probably isn't the scariest thing. So then what is? [projector whirring] Ah. You know what would make this scarier? Perfect. [wolf howling] [fly buzzing] Let's talk about fear of the dark. Children and adults, and myself, often, don't like the dark. - No. - Why? The sensory deprivation. It leads you to feel like you're out of control, like you don't know what's gonna be happening. And, at the same time, predators tend to come out at night, so when we think back to caveman days, they tend to attack later on in the day when you can't see them. And so there's a natural inclination for us to fear the dark, because we don't know what's lurking out there and there's a lot of things that can come and hurt us.

My wife is pregnant right now. I mean, it's pretty dark inside my wife. Is my kid scared of the dark in there? - Nope. Nope. - Why? It's comforting for them. And in fact, if a baby is colicky, they can't be soothed, if you put them in a dark room, they calm down. In fact, this fear of darkness doesn't really come out for most children until about the age of two. That's when, I think, they start to develop certain cognitive and neural memories and maps about things that might be scary about the dark. For example, your parents tend not to be in bed with you necessarily. They're gone. So these are the people who were protecting you. Well, it's dark, you're going to bed and they go to their room and you're by yourself.

So to answer the question, "What's the scariest thing possible," the darkness isn't necessarily the best one, 'cause if a newborn walked in-- well, I don't know how they're walking, but just go with me-- a newborn walks in, it's not gonna be like, "Aah! It's dark!" They'll just be like, "Hmm." Right. "Hmm, it's kinda nice." And you know who else isn't scared of the dark? A blind person. Exactly. So darkness, I'm crossing that off my list. Not universal. - [projector whirring] - [wolf howling] [Michael] So if messing with our sense of sight isn't scary enough, what about our sense of hearing? [woman screaming] Okay, I'm pretty scared right now. But I could be more scared. [man screaming manically] [evil laughter]

[chorus of screaming, cackling] Why is it so easy to condition a fear using sound? Sound has a specific neural pathway in the brain which goes from the auditory cortex, thalamus, straight into the amygdala. Now, the funny thing about sound is, our visual system allows us to see a threat and prepare for it, but sounds don't. The rustle of some leaves, the footsteps in the distance, evokes anxiety, it evokes a situation which we don't know how to respond, because we've not seen a threat yet, we don't know what it is. - Much less information. - Yes.

[thunder crashing] - [animal growls] - [owl hoots] Sound is a very immediate processing within the brain. So a loud sound creates a startle for anybody, immediately. - [staccato chord plays] - But also some of these eerie sounds that you'll hear, they make the hair on the back of your neck stand up, it's basically hijacking your fear system very directly. [ethereal noise echoing] Ch-ch-ch, ah-ah-ah... ch-ch-ch, ah-ah-ah... [Patrick Brice] The first time I heard the "ch-ch-ch... ah-ah-ah, ch-ch-ch," from the Friday the 13th movies, that stuck with me forever. - [gasping] - [man groans] [thunder crashing]

[Sean Cunningham] Music tells you how you're supposed to feel. [slashing violins playing] And I believe that we are hardwired to respond to music. In dramatic musical writing, you can use all kinds of different devices... - [ethereal sounds] - Must be my imagination. ...to create fear. - [slashing violins play] - [screams] Here I am walking through the woods. And here I am walking through the woods... with scary music. [violin playing suspenseful motif] [Michael] But if one note is scary... [introduces dissonant harmonies] ...two notes can be even scarier, especially if they're dissonant. [Dr. Asma] There are certain intervals, two notes that are clashing with each other, that universally bother people. They put you in a kind of almost fight-or-flight situation.

[Michael] Musical intervals that fall outside of conventional harmonies may trigger our innate aversion to things that are different or abnormal. [dissonance continues] This interval, known as the "Devil's Tritone," is so dissonant that composers purposefully use it to make listeners uncomfortable, from TV themes like "The Twilight Zone..." [guitars play dissonant harmony] ...to hard rock like the start of Jimi Hendrix's "Purple Haze." [guitar playing tritone motif] [raven cawing] But music doesn't always have to start out scary. The right context can make even the happiest song absolutely terrifying. [dissonant version of "Pop Goes the Weasel" playing] [music continues, girl humming along] [evil laughter] Once a song has been conditioned to elicit fear, the effect can be extremely strong and long-lasting. For example, the theme song from "The Exorcist," "Tubular Bells." Terrifying, right? Go listen to it, it's scary.

But just a few months before the movie came out, it was a chart-topping pop hit that audiences loved because it was lighthearted and fun. Oh, strawberry. Very good. But here's the problem with sound. Not everyone has been conditioned to be afraid of the same sounds or music, and not everyone can hear-- what about the deaf? Clearly, the scariest thing possible to everyone - will not be a sound. - [girl laughs evilly] Take a look at these paintings. We have a flirty little clown, an abstract piece, and a landscape. Now, these paintings may seem a little bit strange, but I wouldn't say I'm freaked out by them, and I doubt you would either.

But now let me give you a bit more story-- the context behind these items. This picture was painted by John Wayne Gacy, a serial killer who tortured, raped, and killed 33 teenage boys and young men. This was painted by Chares Manson, the infamous cult leader who convinced his followers to commit a series of nine horrific murders in Los Angeles. And this landscape was painted by... Adolf Hitler. Your thoughts about these items have probably changed a bit. Psychologists call this phenomenon the "Law of Contagion." It's our tendency to imbue objects with the qualities of the people they're associated with.

Now, before and after you heard the story, the items were still made of the same molecules and atoms, but our minds use context to quickly endow them with new powers. Now, these paintings cannot hurt you, but the fact that the context allows your amygdala spider to connect them to other fears and, ultimately, through your innate aversions, to death, means they take on a whole new meaning. The right story and context can make almost any object, person, or place scary. In fact, let me ask you a question. What is this, behind me? Ah, you know what? This old camper isn't actually that scary. Ahh, nuts.

All right, things are different now, and I'm starting to feel, yep, an automatic process is already happening to my body. My amygdala now associates this trailer with death and danger. What I'm feeling is actually the same thing that happens when you feel frisson. That's when you're greatly moved by something profound. What's happening is that my amygdala is telling my hypothalamus to tell my adrenal glands to start pumping adrenaline into my bloodstream. This makes my arrector pili muscles contract, which makes my hairs stand up. Now, if my body were covered in thick fur like, say a cat, this would make me look bigger and more threatening.

But of course, a long, long time ago, we humans lost a lot of our fur. But we didn't lose this reflex, which makes it a vestigial reflex, something we don't need anymore but we still have. It is known as the Piloerection Reflex or, more commonly, goosebumps. Anything that's different or abnormal can be scary. Take it, Georgie. [Michael] Like Pennywise in "It," oftentimes the scariest type of predator isn't a human, a creature, or a beast, it's a variation of a human being... [growling] ...a distorted human form that looks, acts, or even moves in a disturbingly unnatural way. Oh, my God.

One thing many of us are terrified by is a distorted human form. Why? Our brain and our mind is a kind of prediction processor. We're trying to predict what's gonna happen next. So when anything comes in and it doesn't match our template, or sense of categories, then we're cognitively and emotionally aroused. So it activates the amygdala, it makes us a little suspicious or at least puts us on our toes again. We have a genetic predisposition to be averse to, or at least aroused by, that which is outside the ordinary. But when you're fresh out of the womb, you don't know what's normal or what's distorted and scary.

Researchers at Princeton and Florida Atlantic University demonstrated this by showing normal faces and creepy, distorted faces... to babies. [Michael] Children that were at least one year old avoided looking at the scary faces, which makes sense. But younger children, like those who were only eight months old, didn't. The hypothesis is that at that age, normal hasn't yet been sufficiently established. A creepy face is just another thing to look at. It only becomes creepy when you've been around long enough to know what's not creepy. So when it comes to finding the one thing that can panic anyone, I'll need to look elsewhere. Because if a newborn baby rolls in here, I won't be able to scare it even with the most vile, scary, unnatural face.

Of course, it's not just faces. Distorted natural forms also include bodies, like humans with other animal parts. [creature growling] Or creatures moving unnaturally. Oh, my. Oh, my. Hoo hoo hoo! "Oh, my," indeed. You know what's going on here, this is the third origin. Fears can be born through firsthand experiences, like feeling pain, or informationally, through stories, but we can also learn fear vicariously by watching others experience fear. [Michael] It's called Social Fear Transmission, and we tried it out during my fear conditioning demonstration. Our unknowing subject was my good friend Alie Ward. Alie was invited to observe my experience and witness my reactions. - [electricity crackling, recorded scream] - [Michael] Jeez! Okay, little bit more scared of the square right now.

[Michael] Right after my test, it was her turn to face the green circle and the purple square that appeared whenever I got shocked. [Dr. Zbozinek] We're gonna use the same shock intensity that Michael had. - Okay. [Michael] Except, that wasn't true. Alie's test would not include any shocks or startling sounds. [Alie] Is it normal to be shaking before this? [laughs] Yeah, it's an anxiety-provoking task. Are you feeling okay about doing it? - Mmm-hmm. Sure. [Michael] Would Alie be afraid of the purple square just from observing my fear of it? - You ready, Alie? - Mmm-hmm. All righty, here we go. I feel like I'm gonna barf.

[Michael] Alie already seems scared. But is she just afraid in general? Or is she more afraid of the purple square? Which shape is making her sweat the most? - That's it? - You're all done. The shock fairy did not come to visit me? The shock fairy did not come to visit you. [laughing] So much adrenaline for no pain. My hands are sweating so much that the dye on my pants is, like, on my hands now. [Michael] So which shape scared Alie more? Despite receiving no adverse stimuli, but after observing my fear, she had a higher physiological response to the purple square than the green circle.

You were definitely more afraid of that purple square throughout the experiment. Ahh. You know, I'm not a gambler, but I think I was thinking, "I haven't gotten shocked yet-- it's coming." People are always saying that they learn from me, but it's usually, you know, math or science or facts in general. You learned fear. I still hate that purple square. You're welcome. [laughing] Let's organize what we've learned so far. Fear is a feeling that we learn to have in response to things our amygdala figures we would do best to avoid because in one way or another, they could lead to our demise.

Strands of fear-silk have connected them in some way to possible death. Now, from talking with experts, in my estimation, there are eight unique innate aversions selected to engender panic in us, by evolution, over millions of years. They come pre-learned in our DNA, and include pain, isolation, the unknown or abnormal, disease, sudden movement, suffocation, falling, and incapacitation. These form the inner ring of the web of fear. All our fears, from rats to radiation, are based on connections made by our amygdalae to death through one or more of these innate aversions. When it comes to learned fears, there may be no limit to the number we can acquire. As long as your amygdala keeps spinning its threads, the web can extend forever.

But here's what's even cooler: when our learned fears are combined just right, they can be scarier than the sum of their parts. Researchers have found that if you've been conditioned to fear two separate stimuli, say, a purple square and a green circle, seeing them suddenly together makes you expect a worse outcome than seeing either stimulus individually. - [Sidney screams] - Horror filmmakers take advantage of this phenomenon by employing a technique called Category Jamming, mashing several categories of fears together to create the scariest villains possible. [Dr. Asma] There's people like Freddy Kreuger, where you've got many things that indicate death and fear, like, you know, the mottled flesh of his skin, the burn, he's a ghost, his hands are blades of some kind. You're weaving together a number of very fearful associations that most people have. - And his criminal past. - Right. All that together. Exactly.

[squishy sounds, whiplash sounds] If you look at, sort of, the Alien franchise, you'll see that the face hugger that grabs onto your face is a beautiful hybrid of a spider and a snake. Those are two things that are universally feared, and so this is a kind of category jamming. It doesn't fit in our categories. The designers basically put them together so the fear is amplified tremendously. Another example could be just taking something that ordinarily would never be here and putting it there. If you put snakes on a plane, you've got something most people are afraid of-- snakes-- you've got flying, which people are afraid of. You've also got strange domain crossing. Why would snakes be on a plane? That doesn't make sense. And that's unsettling in and of itself.

So you're weaving together a number of very fearful associations that most people have, and that's uniquely disturbing, I think. So maybe extreme category jamming, combining every innate aversion and conditioned fear, could be the scariest thing. It would certainly be likely to catch anyone in a web of fear. Let's try it out. Now, conveniently, I'm already in a graveyard, so we already have the fear of death, decay... [church bells tolling] ...it's dark, I'm alone. Let's add in some scary sounds... [wolf howling] [growling] ...a distorted human form, sudden movement... a mortal threat... gore... [creature growling] story and context... [growling] [growls] ...incapacitation. Is this it? Is the scariest thing possible just a combination of every innate aversion and conditioned fear? [laughing]

Oh, dear, Michael. Conditioned fears know no bounds. So the scariest thing is that the human mind can be made afraid of anything! [laughs evilly] No! Noooo! [Michael 3] Hold it! Both of you, stop. Just-- Let's take a step back. Category jamming together every possible learned fear and every innate aversion just sounds like a cop-out. I don't like that. I want to be more specific. But this idea that the scariest thing is the fact that the human mind can be made afraid of anything-- I don't like that, either. I mean, it might be the scariest thing possible... but it also might not. What about people who don't have an amygdala?

Meet Patient SM. Not the snake, the hands. This is all we are allowed to show you. Her amygdala was destroyed at the age of ten due to an incredibly rare genetic disorder. And because she doesn't have an amygdala, she cannot learn to register experiences as threats, which puts her life in danger, and that's why we can't reveal her identity. Patient SM's feelings, the feeling states, her subjective states, seem to be absent in Patient SM. For example, when she was walking through a park one night, a guy came up to her and put a knife to her throat, saying, "Give me your money." And she just kind of ignored them and said, "Well, if you cut me, I'll chase you down and kill you." She was just all rational.

Yeah, yeah. And she apparently kind of knows that this isn't right, but she reacts in a different way. Researchers have even purposefully exposed her to classically scary things, like spiders and snakes and haunted houses and horror films, and she has exhibited no fear response to any of them whatsoever. For a long time, scientists considered SM living proof that without an amygdala, we are unable to feel fear. But then... one experiment changed everything. Scientists have known for decades that a lack of oxygen will make you feel dizzy, and maybe even euphoric, before you pass out. But elevated levels of carbon dioxide in the blood induce fear, anxiety, and panic.

Patient SM volunteered to inhale concentrated CO2. Her brain interpreted the elevated levels of CO2 in her blood as proof that she was suffocating, a process we are innately averse to. As usual, the researchers expected SM to feel no fear. But for the first time in her adult life, she felt sheer and utter panic. The great thing about that study on SM is really it was the first time that we showed that these emotional responses can occur without an amygdala. Over the course of the next year, the scientists tracked down two rare patients in Germany who also had non-functioning amygdalae and gave them the same CO2 inhalation test. They had the same panic response. Researchers believe that the fight-or-flight responses they observed in these amygdala-damaged patients were induced by CO2-sensing neurons in evolutionarily older regions of the brain, like the midbrain or even the brain stem, which control more primal physiological functions.

And so if I want to terrify even the neurologically un-scare-able, I need our body's internal fear response to elevated carbon dioxide levels in the blood. But the story doesn't end there. SM's researchers later discovered something even weirder. When a control group of people with functioning amygdalae inhaled CO2, they showed a lower fear reaction than Patient SM. Why? Well, this question led to a potentially revolutionary rethinking of the amygdala's role in fear. Researches still believe that the amygdala learns to detect threats that are outside the body so that the body can respond to them, but when it comes to internal threats, it may actually inhibit your fear response.

The control subjects knew they were participating in a safe, voluntary experiment, so their amygdalae may have effectively told other parts of their brain, "Hey, relax. Things are bad in the body, but I don't detect a real external threat, so, like, calm down. A panic response isn't gonna help; not warranted." So if you want to ensure the utmost amount of panic in the most people, you don't need to category jam every possible scary and unpleasant thing together, you only need two of them. Increase a person's blood CO2 levels and present an external threat they'll believe is causing it. Drowning. Waterboarding. Coerced CO2 inhalation. They're all variations of the one true scariest thing: elevation of carbon dioxide in the blood caused by an uncontrollable external threat. [snickers] Sweet dreams.

And as always... thanks for watching. ♪ Every single episode of Mind Field ever made is free to view right now on YouTube. Click here to watch the latest season of Mind Field, and click down here to watch other fantastic YouTube originals all about learning. And as always... thanks for watching.